Becoming unresponsive after inactivity

[Zweitaktmotor]

In the past, Sylpheed was not very good at automatically polling inboxes. But at least I knew that I could click on another folder and then back on the inbox and it was updated.

About 6 months ago, a new issue has come up: If I keep Sylpheed open and do not use it for a few minutes, it will no longer download inboxes at all. All I can do is to close the application and restart it. But doing this several times a day becomes abit annoying.

Here is my system info:

version 3.7.0 running under Mint Debiaan Edition 5
my e-mail accounts are hosted on uk2.net

It has perhaps something to do with some setting my e-mail provider has changed on their end, but their support was unable to help.

Any suggestions?

Many thanks.